[amsat-bb] Re: 2m/70cm Quadrifilar Helix antenna Antenna Kit fromAntennas.us
k5oe at aol.com
Tue Apr 26 08:57:09 PDT 2011
Any solution could have benefits, depending on your needs. These antennas would be very stealthy, if deed restrictions are an issue. Also, they are simple (as all omnidirectional antenna) and you would not have to worry about tracking (rotors, software, PC interfaces, etc.).
>From a cost perspective, you could buy a brand new TV rotor, an Arrow or Elk (user's choice, or any similar-gain pair of antennas), and a AAR/SSB/Mirage preamp for less and have a system far superior (~6 dB) in both uplink and downlink capability. Besides just the obvious gain benefit, directional antennas also noticeably reduce local noise/IM exacerbated by a preamp--thus your S/N ratio is also improved dramatically.
If you do want to go with an omni solution, I concur with Mark's suggestion a pair of Tony's parasitic Lindenblad's and a separate RF-sensed preamp would be a good choice. You could build a pair in an afternoon for about $25 in parts and find a used preamp for $75 or so.
UO-14 and SO-35 you could hear easily with an omni antenna. AO-27 you can't. FO-20 was easy to hear, FO-29 not quite so loud. AO-51 when at high power you can hear above 25 degrees with an omni and good preamp, but you will be frustrated by the short pass time available (and when it is set to lower output power). The bottom line is there are no truly "easy-sats" in 2011 and omni antennas are a real compromise that makes operating with them only attractive if there is a good reason you cannot use directioinal antennas. I'll give you a personal example: after moving back to Texas late last year I wanted to get back on the birds, so I "threw" up an old omin antenna (Eggbeater II from a long, long time ago) and put a Landwehr preamp in the attic (it was easy and fast). See my comment above about being frustrated--I didn't operate much. When ND9M was at sea I got really frustrated! So I swapped out the Egg II with a slightly-less old antenna, a TPM II and pointed it due West (fixed, no rotor) and worked Jim a few times, mostly on FO-29, when he was in the Pacific Ocean. After he went through the Panama Canal, I went back on the roof and pointed the antenna to the SE and worked him a few more times in the Carrib and GoM. I worked him in 9 grids, but was not able to work much else. Last weekend I finally made the time to run the cables through the house walls for the rotor and quickly built up a small homebrew beam for 70 cm (3x3), installed a coaxial relay for polarity switching, and moved the preamp to just below the antenna: a world of difference, as you can imagine. Solid copy on all those birds now. Sorry for the long story, but my recommendation is borne out of experience--only use the omni if you can't use a beam.
--- original message ---
I would ask them about transmitting through the one with the preamp built in.
Can you do it? (i.e., is it RF-sensed/switched)
Or does the preamp make it a "receive only" antenna, with the accidental
transmission through it smoking the device :) It's bound to happen on a dual
(I think you'd be better off building a pair of AA2TX style Lindenblads...)
At 12:01 PM 4/25/2011 +0000, vtnn43e at comcast.net wrote:
>Antennas.us is selling a combo package of 2M and 70cm quadrifilar helix
>antennas and a bias tee for $330.00. The 70cm antenna has a built-in 15db LNA
>The UC-AMSAT-KIT, 2 m / 70 cm Amateur Satellite Antenna Kit is a discounted
>bundle combination of quantity 1 each of the following three antenna products:
>UC-1464-433, VHF Amateur Satellite QFH Antenna, Passive
>UC-4364-513, UHF Amateur Satellite QFH Antenna, with built-in LNA and SMA Male
>BIT-1500-385, UHF Bias Tee
>I was wondering though what some of you on the list think of these antennas
>for FM LEO users that are looking for fixed outdoor antennas?
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